In various industrial, agricultural, culinary, and pharmaceutical applications, it may be required to ship or otherwise transport products at temperatures less than or greater than the ambient temperature, in order to avoid spoilage or other degradation. For example, pharmaceutical items such as vaccines and other biological substances are particularly sensitive to thermal variation during shipment, and must be contained in a highly thermally controlled environment. Likewise, fresh food products may require a specified temperature range during transport in order to obtain the maximum shelf-life upon arrival at their point of sale.
Many such products are required by law to be stored and shipped in what is known in the art as a “cold chain.” A cold chain is an unbroken, temperature-controlled supply chain of storage and distribution which originates at the point of manufacture and terminates at the end consumer. For example, the Food and Drug Administrative enforces strict cold chain requirements on the storage and distribution of drugs and other biological products in order to ensure their safety, efficacy, and quality.
One approach to a cold chain is to use packaging that is insulated and has thermal control devices that can be cooled and packaged with the contents to hold the package contents at a targeted temperature range. Existing thermal-control devices suffer from a variety of inefficiencies and problems in field use. For example, gel-based devices, e.g., filled plastic bags, are not suitable for some applications, as “slumping” may occur in the shape of these devices during phase change. Dry ice blocks may sublimate during shipping, causing carbon dioxide to accumulate at pressure—many forms of transportation, such as air transportation, require dry ice containers to carry special warning labels. Wet ice is prone to leakage when not handled properly, and it is inefficient at maintaining temperature for more than short periods of time.
Further, existing thermal-control devices may be inappropriate for transportation or shipping that requires a precise thermal range. For example, dry ice sublimates at −78.6 degrees Celsius, and must be kept at a distance from the product within the packaging for typical applications which require the temperature to be maintained between −15 and −5 degrees Celsius in order to avoid damaging the product. This concern is particularly prevalent in the pharmaceutical industry, which often requires shipment of biological products within a temperature range covering just a few degrees Celsius.
Phase change materials are known in the art as materials which use changes in physical phase to absorb or release heat at a relatively constant temperature. Typically, phase change materials undergo the physical transformation known as fusion (freezing/melting), which carries an associated latent heat. Known phase change materials include salts, hydrated salts, fatty acids, and paraffins, among others. Such phase change materials, suitably packaged, may be used as thermal devices.
Unlike dry or wet ice, most phase change materials are not readily adaptable for shipping and transportation applications by themselves. They must be adapted to a substrate or other carrier which contains the phase change material in a defined form and at a defined location within the packaging. This additional requirement has led to inefficiencies in existing phase change devices, such as cooling capacity and weight-to-volume characteristics, which are particularly important concerns for shipping and transportation. For some phase change materials a porous substrate has been used as an absorbing and carrying medium. In U.S. Pat. No. 6,765,031, a micropore open cell foam is used. In some embodiments absorption of the phase change material into the foam is driven by application of vacuum and greater-than-atmospheric pressure.
What is needed in the art is an improved thermal control phase change device, and methods for making the same, suitable for use in packaging for the shipment and transportation of temperature sensitive products.